The present invention relates to xe2x80x9cactive implantable medical devicesxe2x80x9d as such devices are defined by the Council of the European Communities"" Jun. 20, 1990, Directive No. 90/385/CEE, more particularly to pacemaker devices, including xe2x80x9cmultisitexe2x80x9d pacing devices (triple or quadruple chamber), defibrillators and/or cardiovertors, which devices are able to deliver to the heart low energy pulses for the treatment of heart rate disorders. The invention also relates more particularly to those active implantable medical devices which include stimulation circuits having an automatic mode switching (AMS) operation, as described, for example, in EP-A-0 488 904 (and its corresponding U.S. Pat. No. 5,318,594) (commonly assigned herewith to ELA Medical, Montrouge, France).
Active implantable medical devices are known which include means for providing the stimulation and detection at the same time on the atrium and the ventricle, that can operate in two operating modes, DDD or AAI (the AAI mode being a DDD mode having a lengthened atrio-ventricular delay (AVD)), with automatic switching from one operating mode to the other. The basic operating mode is the AAI mode, with single chamber atrial stimulation. This AAI mode is maintained as long as atrio-ventricular conduction is normal, i.e., as long as each atrial event (detection, corresponding to a spontaneous activity, or stimulation) is followed by an associated ventricular detection.
In certain circumstances, in particular during episodes of effort (i.e., when the patient is active and not at rest), atrio-ventricular blocks (AVB), known as xe2x80x9cparoxystic blocksxe2x80x9d, involving a depolarization defect of the ventricle, can appear. In such a case, the pacemaker switches into an automatic DDD operating mode, with parameters optimized for a temporary AVB situation. Preferably, to favor a return of spontaneous atrio-ventricular conduction, the pacemaker applies a relatively long atrio-ventricular delay in order to allow for a spontaneous atrio-ventricular (AV) conduction of the patient to occur before a ventricular stimulation is delivered.
After the disappearance of the AVB, and thus after a reestablishment of spontaneous AV conduction, the pacemaker automatically returns to the AAI operating mode, since a certain number of corresponding conditions have been fulfilled, as described in the aforementioned patent.
Thus, the control algorithm for the automatic mode switching (herein the xe2x80x9cDDD ASMxe2x80x9d algorithm), in order to favor the occurrence of spontaneous conduction, uses a rather long conduction delay value (also known as the atrio-ventricular delay or xe2x80x9cAVDxe2x80x9d) before switching to deliver a ventricular stimulation. The time between the atrial event and the consecutive ventricular detection is known as the xe2x80x9cconduction intervalxe2x80x9d or xe2x80x9cconduction timexe2x80x9d, namely, the xe2x80x9cPR conduction intervalxe2x80x9d for the time between an atrial detection and a corresponding consecutive ventricular detection, and the xe2x80x9cAR conduction intervalxe2x80x9d for the time between an atrial stimulation and a corresponding consecutive ventricular detection.
Indeed, it is desirable to let a spontaneous AV conduction occur, and generally preferable from a physiological point of view (better filling of the cardiac cavities, etc.), in comparison to a stimulated operation.
The starting point of the present invention is the observation by the applicants that, in certain cases, it is not always desirable to try to let the spontaneous AV conduction of the patient occur. Indeed, there are certain types of AVB for which the AV conduction defects of certain patients can result in an absence of the reduction (and even a lengthening of same) of the PR (or AR) conduction time during a patient effort. Such a conduction exists, but it is not hemodynamically good, and it would therefore be preferable instead to stimulate the ventricle.
The present invention, therefore, proposes an improved method and device making it possible to diagnose whether the adaptation of the conduction time during a patient effort is a good adaptation or a bad adaptation, i.e., beneficial or not beneficial to the patient, and to cure bad adaptation situations by suitable modifications of the pacemaker operating parameter(s). The type of device to which the invention applies is a DDD ASM type device, as described, for example, in EP-A-0 488 904 and U.S. Pat. No. 5,318,594 mentioned above. Such a device includes means for sensing atrial and ventricular spontaneous events, means for detecting the presence or the absence of an atrio-ventricular spontaneous conduction and means for delivering ventricular and atrial stimulation, the ventricular stimulation being applied in the absence of a detection of a spontaneous atrio-ventricular conduction, after the completion of a programmed atrio-ventricular delay started on a spontaneous or stimulated atrial event. Such means are well known in the art and any suitable circuit, logic devices and software may be used.
According to the present invention, this device further includes functionality and/or means to discriminate between phases of effort and rest of the patient bearing the device, means for measuring an atrio-ventricular conduction time separating a spontaneous or stimulated atrial event and a corresponding consecutive spontaneous ventricular event, and a means for diagnosing a good or a bad adaptation of conduction time during the patient effort. The diagnosing means operates by evaluation, during the phase of patient effort, of the conduction time variation in relation to any heart rate variation.
Very advantageously, the device of the present invention responds to a diagnosis of a bad adaptation of the conduction interval during an effort, by deactivating the automatic mode switching of the device, and switching the device to operate in a DDD mode and reprogramming the atrio-ventricular delay with a value that is shorter than the value previously programmed.
Preferably, discriminating between phases of effort and rest of the patient is achieved by use of an activity sensor which responds to the patient""s level of effort.
In one embodiment, the diagnosis means is activated only if, during the phases of evaluation, the atrial events are either all spontaneous events or all stimulated events. Further, the diagnosis means preferably determines that there is a bad adaptation during an effort when the aforementioned evaluation reveals an absence of a reduction of the conduction time when there is an increase in the heart rate.
The above-mentioned evaluation is preferably operated by memorizing successive determined values of the conduction time, or by memorizing averages of the successive determined values. The values are measured for a plurality of successive predetermined heart rate values, and the values of the measured conduction time are possibly retained for evaluation only when they are included within a predefined range around the corresponding predetermined heart rate.
In one embodiment, the diagnosis means is activated if the increase in the heart rate from the beginning of the phase of effort is greater than a predetermined threshold. Further, in yet another embodiment, there is provided means for limiting the value of the atrio-ventricular delay in the phase of effort when the heart rate becomes greater than a predetermined threshold.
In yet another embodiment, the diagnosis means determines that there is a bad adaptation during the effort when, for a predetermined number of cardiac cycles presenting a frequency greater than a predetermined heart rate, the conduction time is greater than a predetermined maximum duration.
Preferably, the de-activation of the automatic mode switching, the switching into DDD operating mode, and the reprogramming of the atrio-ventricular delay are operated throughout the duration of the phase of effort, with the former mode of operation being restored only after return of the patient""s activity to a rest phase.